Method for treating acrylonitrile polymer fibers to improve heat stability



United States Patent 3,296,348 METHOD FOR TREATING ACRYLONITRILE POLYMERFIBERS TO IMPROVE HEAT STA- BILITY John Moore, Williamsburg, Va.,assignor to The Dow Chemical Company, Midland, Mich., a corporation of IDelaware No Drawing. Filed Aug. 23, 1963, Ser. No. 304,206 Claims. (Cl.264182) spinning techniques and are in a highly swollen, or gelcondition.

Acrylonitrile polymer fibers containing at least about 80 weight percentof polymerized acrylonitrile are particularly adapted for thepreparation of synthetic fibers and filaments. While the properties ofthese acrylonitrile polymers are well suited for textile fiber purposes,it has been observed that such polymers have a tendency to be somewhatheat sensitive and to discolor and become stiff or brittle whensubjected to elevated temperatures.

It can well be appreciated that these degrading factors should beavoided, if at all possible, in that textile products are quite apt tobe subjected to high temperatures in processing and subsequent use,including dyeing, drying, laundering, and pressing, or ironing. Whilethe heat sensitivity of some of the polymers may only lead todiscoloration, and not to the point of causing embrittlement of thefibers, discoloration itself is an especially undesirable feature whenwhite or faintly colored fabrics of the fibers of filaments is desired.

The tendency of fibers from acrylonitrile polymers to discolor whenexposed to heat is often more pronounced and more frequently encounteredwhen homopolymeric acrylonitrile is used as the sole fiber formingpolymer. When copolymers of acrylonitrile and another ethylenicallyunsaturated monomer are extruded into fibers, it is frequently notedthat these fibers may be more heat resistant. The reasons for this arenot fully known, but it is a likely theory-that the other monomers inthe polymer chain aid in proving heat stability to the fibers formedfrom these polymers. It has been observed also that discoloration ofacrylonitrile polymer fibers occurs more frequently in polymers that arespun from aqueous saline solutions that are solvents for the polymersthan from organic solvents.

It is the chief concern and primary object of this invention to providea means for improving the stability of wet spun acrylonitrile polymerfilaments. It is a further object of the invention to improve the heatstability of acrylonitrile polymer filaments that have been wet spunfrom aqueous saline solutions of the polymer. In a more particularaspect, it is the object of this invention to provide a means forpreparing acrylonitrile polymer fibers having improved heat stabilitythat have been spun from aqueous solutions of zinc chloride into anaqueous coagulation bath. It is a still further object of the inventionto treat wet spun homopolymeric acrylonitrile polymer fibers to improvetheir heat stability.

The foregoing and additional objects and advantages of the invention areachieved in and by the practice of the present invention, which involvesthe method for preparing acrylonitrile polymer filaments having improvedheat stability comprising impregnating a wet spun gel filament of anethylenically unsaturated monomeric ma, terial containing :at leastabout weight percent of acrylonitrile with a water soluble zirconiumsalt such that between about 0.1 and about 2 weight percent ofzirconium, based on dry fiber weight, is incorporated in said filament.In a preferred embodiment of the invention the wet spun lgel filamentsare impregnated with a water soluble zirconium salt after the gelfilament has been washed essentially completely free of any residualpolymer solvent.

The acrylonitrile polymer fibers or filaments treated in accordance withthe present invention have excellent and much improved heat stabilityover the untreated fibers, and the fibers so treated remain unchanged incolor even after extended exposure times to elevated temperatures.Additionally, the presence of the zirconium salt in the fiber has noapparent deleterious elfects on the properties or utilities of theimpregnated fibers. The zirconium salts with which the fibers areimpregnated are unusually compatible with an adherescent to the fibers,either being chemically or physically entrapped in the fiber, such thatlasting and essentially permanent heat stability properties are observedin the impregnated fibers.

The zirconium salts found useful for enhancing the heat stability of theacrylonitrile polymer fibers are those having some water solubility.These need not be infinitely water soluble, but only to a small extentsince the impregnation of the fibers is ordinarily accomplished with arelatively dilute solution of the zirconium salt. Thus, exemplary ofsome of the zirconium salts that can be employed in the presentinvention are zirconium tetrachloride, zirconyl chloride, zirconyltetrabromide, zirconyl nitrate, carbonated hydrous zirconia, zirconiumsulfate, zirconium acetate, including their partially hydrolyzed andpartially neutrallized forms. Advantageously, zirconium oxychloride orzirconyl chloride is employed.

The amount of the zirconium salt that is impregnated or otherwiseincorporated in the fiber is beneficially enough to incorporate in thefiber between about 0.01 and about 2 Weight percent zirconium, based onthe Weight of the dry fiber. Preferably, between about 0.3 and 0.75weight percent zirconium is impregnated in the fiber. It

is generally desirable to employ as little as possible of the zirconiumsalt that is called for to obtain the desirable or necessary heatstability. In order to impregnate the acrylonitrile polymer gel filamentwith the zirconium salt, only a relatively dilute solution of the saltis necessary, as indicated. Thus, generally a solution containingbetween :about 0.1 up to about 1.5 or so percent of the zir conium saltis adequate to deposit the required amount of zirconium in the fiber.Solutions containing concentrations of the zirconium salt up to thesaturation concentration of the salt can be employed, but, beneficially,solutions containing between 0.5 and 1.5 weight percent of the zirconiumsalt are used to avoid undue accumulation of the salt in and on thefiber which may deleteriouly elfect the properties or end uses to whichthe filaments or fibers can be put. The amount of the salt that isincorporated in the fiber can be controlled by the concentration of theimpregnation bath that is employed, as well :as the speed with which thefibers pass through the impregnation bath.

The impregnation of the gel filament is preferably accomplished from anaqueous solution of the zirconium 'parts by weight of water for salt.The impregnation, can, if desired, be carried out by spraying, paddingor wiping the gel filaments'with an aqueous solution of the zirconiumsalt, however, best results are obtained when the impregnation isperformed by immersing the gel filaments in an aqueous solution of thezirconium salt. This is conveniently done under conventional wetspinning conditions and at conventional spinning rates. Thus, inordinary wet spinning techniques, the wet spun fiber is withdrawn fromthe coagulation bath, washed essentially completely free of any residualpolymer solvent, and then stretched to orient the molecules of the fiberto impart suitable physical properties to the fiber. to the conventionalwet spinning techniques in that excellent impregnation of the zirconiumsalt results when the gel filaments are continuously passed through anaqueous bath containing the zirconium salt, which impregnation can becompleted in a matter of seconds. In practice, the impregnation of thefiber with the zirconium salt can be accomplished before-,during, orafter the orientation of the fiber molecules. Most generally, however,the impregnation always succeeds the washing of the gel filament free ofresidual polymer solvent.

The temperature of impregnation is not critical and may be at ambienttemperature, or lower, up to the boil of the impregnating solution.

The invention is applicable to treating acrylonitrile polymer fiberswhich are fabricated from fiber forming acrylonitrile polymers thatcontain in the polymer molecule at least about 80 weight percent ofpolymerized acrylonitrile, and is especially applicable to treatingfibers of homo- The present method is therefore well suited 7 polymericacrylonitrile, which are wet-spun in and with I systems that are adaptedto utilize aqueous coagulating liquids in the spinning operation, suchas systems wherein ethylene glycol, dimethylformamide,dimethylacetamide, dirnethylsulfoxide, butyrolactone and the like or thevarious saline polyacrylonitrile-dissolving solvents are em ployed asspinning solution solvents for the polymer and are also present innon-polymer dissolving quantities in the aqueous coagulating liquid usedin the spin bath;

The utile, known aqueous saline solvents for the various fiber formingacrylonitrile polymers and polyacrylonitrile include zinc chloride, thevarious thiocyanates such as' calcium and sodium thiocyanate, lithiumbromide, salt mixtures of the so-called lyotropic series, and othersrecognized by the art as has been disclosed, among other places, inUnited States Letters Patents Nos. 2,425,192;

and 2,949,435. Advantageously, aqueous'zinc chloride solutions are usedfor the purpose.

Exemplary of some of the monomeric materials that may be employed withthe acrylonitrile in the preparation of the acrylonitrile polymer andcopolymer fiber forming systems and treated in accordance with thepractice of .the present invention include allyl alcohol, vinyl acetate,acrylamide, methacrylamide, methyl acrylate,

vinyl pyridine, ethylene sulfonic acid and its alkali metal salts, vinylbenzene sulfonic acid and its salts, 2-sulfo-' ethylmethacrylate and itssalts, vinyl lactams such as vinyl caprolactam and vinyl pyrrolidone,etc. and mixtures thereof. I

As indicated, after acrylonitrile polymer fibers have 'been wet spunthey are most frequently water washed or washed with an aqueous inertsolution to remove any residual polymer solvent from the freshly formedfilaments, thus forming an intermediate fiber product often referred toas a gel or aquagel filament. Thoroughly washed acrylonitrile polymeraquagel fibers, incidentally, are usually found to contain up to about 6parts by weight of water (including residual extrinzic or exterior waterassociated therewith) for each part by weight of dry polymer therein.More frequently, washed acrylonitrile aquagel polymer fibers are foundto contain from about 3 to 4 each part by weight of polymer.

Example 1 Acrylonitrile polymer fibers consisting of about, incopolymerized form, 91.5 percent acrylonitrile, 7 percent methylacrylate and 1.5 percent 2-sulfoethylmethacrylate were prepared byspinning a solution of the polymer dissolved in an aqueous about 60weight percent zinc chloride solution into an aqueous zinc chloridecoagulation bath. The coagulated gel filaments were withdrawn from thecoagulation bath, washed essentially completely free of residual zincchloride and hot stretched to orient the molecules thereof. The washedand stretched 'gel fila- 'rnents were then passed through an aqueousabout 1 percent solution of various zirconium salts to impregnate thegel filaments therewith. The impregnation was carried out in acontinuous manner by passing the gel filaments through a bath containingthe zirconium salt solution which was at about 30 C. The residence timeof the gel filaments in the bath was about 5 seconds. Following theimpregnation the gel filaments were ultimately irreversibly dried 6-7minutes at about 125 C. to characteristically hydrophobic textilefibers.

Control'fibers were prepared in'the same manner, the only differencebeing that no zirconium salt was present in the impregnation bath. I V aSamples of each of the fibers so-prepared were cut into short staplelengths and formed into an aqueous slurry in a Waring Blender. Theslurry was poured through a filter to form a pad of the fibers which wasdried leaving about a inch thick pad of the fibers. The pad was thenpressed between two metal plates of an AATCC Scorch Tester at 205 C. for5 minutes. The measuring head of a Photovolt Corporation reflectorneterfitted with a green tristimulus filter was first placed on-theunscorched portion of the pad and the instrumentadjustedto a reflectancereading of a reflectancereading was then taken on the scorched portionof the fiber pad. The difference in reflectance is a measure of thecolor formation.

due to heat. The recorded values are the number of units below thecontrol value of 100. The smaller the recorded value the less changefrom the unscorched reading of 100 and hence the better the heatstability of the fiber. The results are set forth in Table I.

The procedure of Example I was repeated excepting to employ airqonylchloride in the impregnating solution at various concentrations. Theseresults are set forth in Table II.

TABLE 11 Percent Percent Zirconium in Sample ZIOClz-SH O Fiber (basedHeat Stability in Solution on fiber dry Reading weight) A 63 B 0. 0. 72235 0 0 65 0. 5 0. 525 35 C 0 0 65 0. 5 0. 449 21 D 0 0 77 l. 0 1. 28 E 00 59 l. 0 0. 79 26 F 0 0 38 1. 0 0. 47 25 G 0 0 53 1. 0 0. 989 24 H 0 062 1. 5 0. 396 17 I 0 O 63 1. 5 0. 629 22 J 0 O 53 1. 5 0. 625 17Example 3 The procedure of Example I was repeated employing zirconylchloride and zirconium sulfate solutions of varying concentrations.These results are set forth in Table III.

TABLE HI Salt Solution Wt. Percent Zirconium Salt Concentration Zr inFiber Heat Stabillty (Wt. Percent) (Based on Fiber Reading Z Dry Wt.)

ZrO ClrSHzO 0. 0 54 0. l. 0. 537 46 2. O 0. 81 30 3. 0 0. 86 29 5. 0 1.04 29 10. 0 1. 19 30 20. 0 1. 48 27 HzZtO (504)2-3Hz0 0. 0 54 0. 1 0.309 37 1. 0 0. 413 27 2. 0 0. 47 40 3. 0 0. 54 34 5. 0 0. 68 34 10. 0 0.94 33 20. 0 1. 16 29 Example 4 Fibers were prepared and treated withzirconyl chloride following the procedure of Example I except the fiberswere homopolymeric acrylonitrile. These results Similar excellentresults are obtained when the foregoing is repeated in accordance withthe present invention employing other of the indicated zirconiumcompounds and acrylonitrile polymer compositions.

What is claimed is:

1. The method for preparing an acrylonitrile polymer fiber havingimproved heat stability comprising impregnating a wet spun gel filamentof an ethylenically unsaturated monomeric material containing at leastabout weight percent acrylonitrile with a Water soluble zirconium saltuntil between about 0.01 and about 2 weight percent of zirconium, basedon dry fiber Weight, is incorporated in said filament.

2. The method of claim 1, wherein said acrylonitrile polymer ispolyacrylonitrile.

3. The method of claim 1, wherein said gel filament is impregnated withsaid zirconium salt by immersing said gel filament in an aqueoussolution of said zirconium salt.

4. The method of claim 1, wherein said zirconium salt is zirconylchloride.

5. The method for preparing an acrylonitrile polymer fiber havingimproved heat stability comprising (a) spinning a solution of a polymerof an ethylenical- 1y unsaturated monomeric material containing at leastabout 80 weight percent acrylonitrile dissolved in a solvent thereforinto an aqueous coagulation bath;

(b) withdrawing a coagulated gel filament from said coagulation bath andwashing said gel filament essentially completely free of any residualpolymer solvent;

(c) impregnating said washed gel filament with an aqueous solution of awater soluble zirconium salt until between about 0.01 and about 2 weightpercent of zirconium, based on dry fiber weight, is incorporated in saidfilament; and,

(d) subsequently, irreversibly drying said gel filament to acharacteristically hydrophobic textile fiber.

6. The method of claim 5, wherein said acrylonitrile polymer ispolyacrylonitrile.

7. The method of claim 5, wherein said zirconium salt is zirconylchloride.

8. The method for preparing an acrylonitrile polymer fiber havingimproved heat stability comprising (a) spinning a solution of a polymerof an ethylenical- 1y unsaturated monomeric material containing at leastabout 80 weight percent acrylonitrile dissolved in an aqueous about 55to 65 weight percent zinc chloride solution into a coagulation bath ofan aqueous non-polymer dissolving zinc chloride solution;

(b) withdrawing a coagulated gel filament from said coagulation bath andwashing said gel filament essentially completely free of residual zincchloride;

(c) immersing said gel filament in an aqueous solution of a Watersoluble zirconium salt until between about 0.01 and about 2 weightpercent of Zirconium is incorporated in said filament; and,

(d) subsequently, irreversibly drying said gel filament to acharacteristically hydrophobic textile fiber.

9. The method of claim 8, wherein said acrylonitrile polymer ispolyacrylonitrile.

10. The method of claim 8, wherein said zirconium salt is zirconylchloride.

References Cited by the Examiner UNITED STATES PATENTS 2,482,816 9/ 1949Van Mater 260414 2,661,346 12/1953 Wesp et al. 26045.75 2,668,780 2/1954Panik et al l17--138 2,813,845 11/1957 Wesp et al. 26045.75 3,097,0547/1963 Routson et al. a; 264-182 ALEXANDER H. BRODMERKEL, PrimaryExaminer.

B. SNYDER, Assistant Examiner.

1. THE METHOD FOR PREPARING AN ACRYLONITRILE POLYMER FIBER HAVINGIMPROVED HEAT STABILITY COMPRISING IMPREGNATING A WET SPUN GEL FILAMENTOF AN ETHYLENICALLY UNSATURATED MONOMERIC MATERIAL CONTAINING AT LEASTABOUT 80 WEIGHT PERCENT ACRYLONITRILE WITH A WATER SOLUBLE ZIRCONIUMSALT UNTIL BETWEEN ABOUT 0.01 AND ABOUT 2 WEIGHT PERCENT OF ZIRCONIUM,BASED ON DRY FIBER WEIGHT, IS INCORPORATED IN SAID FILAMENT.